1. Field of the Invention
The present invention deals with railway control and, more particularly, to code following apparatus, such as code following track relays, for receiving pulsating rail current from a railway code transmitter.
2. Background Information
A conventional railroad track circuit typically includes a battery, a resistor, a track, and a relay. The feed or battery end and the relay end of the track circuit are electrically connected to the two rails of the track. Under conditions when a vehicle, such as a train, is not within the track circuit, the battery energizes the coil of the relay through the series combination of the-resistor, the first rail, the coil and the second rail. In turn, the normally open contact of the energized relay closes. The track circuit employs the shunting properties of the train""s wheels and axle (i.e., a train shunt) to sufficiently reduce the current in the relay coil and, thus, open the normally open contact, in order to indicate the presence of the train in the track circuit.
As shown in FIG. 1, a conventional code following railway track relay (TR) 2 is used in a railway track circuit 3 in which a low voltage battery source 4, at one end 6 of the circuit, is interrupted at a low frequency (e.g., generally less than about 3 Hz) by a conventional railway code transmitter 8. At the other end 10 of the track circuit 3, the code following track relay 2 responds to the pulsating current on the rails 12,14, thereby opening and closing its contacts 16. The series combination of a resistor 18, the low voltage battery source 4 and the railway code transmitter 8 are electrically connected to the rails 12,14 at the one circuit end 6. The series combination of a resistor 20 and the coil 22 of the track relay 2 are electrically connected to the rails 12,14 at the other circuit end 10.
Typically, the coil resistance of code following relays, such as TR 2, is typically in the order of about 0.5 xcexa9, with operating current being in the order of 0.5 A. Again, because code following relays are electro-mechanical devices and operate constantly, they are subject to wear. Particularly, the contacts, such as 16, pit and erode from constant electrical switching. For safety reasons, it is important for the relay operating current to remain relatively stable. If it were possible for the operating current to reduce significantly, then a broken rail could go undetected and, thus, jeopardize train safety. Periodic re-calibration to ensure consistency of the operating current is the process by which safety is assured.
As employed in railway signaling, the dynamic action of the code following relay indicates that the particular track circuit is not occupied. If the relay is not responding to the dynamic action of the rail current, then the particular track section is occupied. Hence, restrictive signals are displayed in order that a train has sufficient distance to stop.
In such railroad code following relays, the term xe2x80x9cBACKxe2x80x9d corresponds to relay contacts that are closed when the relay is de-energized. Similarly, the term xe2x80x9cFRONTxe2x80x9d corresponds to relay contacts that are closed when the relay is energized.
In general, electro-mechanical relays wear out after long periods of constant cycling. In particular, code following railway track relays suffer the same problem.
There is a need, therefore, for a circuit that improves the reliability of code following railway track relays after long periods of constant cycling.
U.S. Pat. No. 3,661,089 discloses a code reader for an automated vehicle, which moves along a path having a plurality of magnetic code elements located at sensing stages along the path. The code reader includes a plurality of Hall-effect devices. For each of the Hall-effect devices, a pulse driving circuit couples an actuating pulse of current through the device terminals responsive to a common pulse generator. A difference amplifier is coupled across the output electrodes of each of the Hall-effect devices. The difference amplifier produces a positive or negative potential output signal based upon the magnetic orientation of the magnetic code elements. Bipolar outputs provide a logic level xe2x80x9c1xe2x80x9d for respective positive and negative potential output signals, again based upon the magnetic orientation of the magnetic code elements. A downstream control system preferably includes error-detecting circuitry to detect the occurrence of two simultaneous logic level xe2x80x9c1xe2x80x9d output signals from the same sensing state.
U.S. Pat. No. 4,415,134 discloses a Hall effect track circuit-receiving element. Wires are connected to two track rails and are series-connected with a Hall effect cell through a switch. The Hall effect cell includes a coil forming a part of an electromagnetic device, which is located within the cell. A receiver receives its input from the Hall effect cell along output lines.
U.S. Pat. Nos. 4,498,650; and 4,451,018 disclose a toroid including a first conductor forming a winding, which is coupled to track rails via a switch. The MMF of one of two polarities is induced in the toroid depending on whether one of two check winding conductors is energized. An air gap in the core of the toroid has a Hall sensor located therein to respond to the MMF induced in the core as a result of current flowing in any of the conductors. In turn, the Hall sensor provides an output voltage.
U.S. Pat. No. 4,320,880 discloses an electronic track current switching relay system, which emulates the operation of a polar relay for applying coded pulses to railway tracks. A timer circuit includes a high-limit threshold circuit and a low-limit threshold circuit, which trigger a flip-flop or latch.
U.S. Pat. No. 4,935,698 discloses a dual-Hall integrated circuit (IC) including two essentially identical Hall elements, which are connected in series. In the IC, the outputs of the two Hall elements are differentially connected to the input of a differential amplifier, in order that the output voltage is a function of the difference between the magnetic fields at the Hall elements. The output of the amplifier is connected to the input of a Schmidt trigger circuit having an output connected to the IC output terminal. The IC and a magnet form a proximity sensor.
U.S. Pat. No. 4,737,710 discloses a Hall-effect position sensor apparatus, which senses the position of a moving body and provides an output signal indicative of the position of the moving body. The apparatus includes a predetermined number of Hall-effect sensors, which are positioned in a straight line and in operating proximity to a moving body made of a ferromagnetic material.
U.S. Pat. Nos. 5,694,038; and 6,232,768 disclose a Hall element having an output connected to the input of a Hall voltage amplifier. The Hall element may be mounted at a pole of a magnet, in order that when a ferrous article approaches, the Hall voltage and, thus, the amplified Hall voltage increase (or decrease depending on the polarity of the magnet pole).
The present invention employs a Hall effect digital current sensor, which has a Hall sensor in the gap of a toroid, in order to turn on and off in response to pulsating rail current. This provides electrical isolation of rail current to downstream solid state switching devices that function like the mechanical contacts of an electro-mechanical relay.
As one aspect of the invention, a code following apparatus for receiving pulsating rail current from a railway code transmitter comprises: first and second inputs structured to receive the pulsating rail current; two Hall effect digital current sensors, each of the Hall effect digital current sensors having a coil and an output, which responds to current flowing through the coil, the coils of the Hall effect digital current sensors being electrically connected in series between the first and second inputs and being structured to receive the pulsating rail current, the outputs of the Hall effect digital current sensors being structured to turn on and off in response to the pulsating rail current; means for determining that each of the Hall effect digital current sensors is functional; and at least one output structured to follow the pulsating rail current.
The output of the Hall effect digital current sensors may have a signal with a plurality of positive going edges and a plurality of negative going edges in response to the pulsating rail current. The means for determining may comprise first and second one-shot multivibrators, the one-shot multivibrators having an input, which is connected to a corresponding one of the outputs of the first and second Hall effect digital current sensors, the one-shot multivibrators further having an output, the output of the first one-shot multivibrator responding to the positive going edges of the first Hall effect digital current sensor, and the output of the second one-shot multivibrator responding to the negative going edges of the second Hall effect digital current sensor.
The means for determining may further comprise a flip-flop including a set input, a reset input and an output. The output of the first one-shot multivibrator may be electrically interconnected with the reset input of the flip-flop, and the output of the second one-shot multivibrator may be electrically interconnected with the set input of the flip-flop.
The output of the flip-flop may have an alternating signal with a set state and a reset state, the alternating signal indicating that the first and second Hall effect digital current sensors are functional.
The output of the flip-flop may have a static signal with one of a set state and a reset state, the static signal indicating that at least one of the first and second Hall effect digital current sensors is not functional.
As another aspect of the invention, a solid state code following track relay for receiving pulsating rail current from a railway code transmitter comprises: first and second inputs structured to receive the pulsating rail current; two Hall effect digital current sensors, each of the Hall effect digital current sensors having a coil and an output, which responds to current flowing through the coil, the coils of the Hall effect digital current sensors being electrically connected in series between the first and second inputs and being structured to receive the pulsating rail current, the outputs of the Hall effect digital current sensors being structured to turn on and off in response to the pulsating rail current; means for determining that each of the Hall effect digital current sensors is functional; and at least one solid state output structured to follow the pulsating rail current.
The output of the Hall effect digital current sensors may have a signal with a plurality of positive going edges and a plurality of negative going edges in response to the pulsating rail current. The means for determining may comprise first and second one-shot multivibrators, the one-shot multivibrators having an input, which is connected to a corresponding one of the outputs of the first and second Hall effect digital current sensors, the one-shot multivibrators further having an output, the output of the first one-shot multivibrator responding to the positive going edges of the first Hall effect digital current sensor, and the output of the second one-shot multivibrator responding to the negative going edges of the second Hall effect digital current sensor. The means for determining may further comprise a flip-flop including a set input, a reset input and an output. The output of the first one-shot multivibrator may be electrically interconnected with the reset input of the flip-flop, and the output of the second one-shot multivibrator may be electrically interconnected with the set input of the flip-flop.
The first and second output circuits may comprise means for outputting a first signal and means for outputting a second signal, which is a substantially inverted version of the first signal, respectively. The first and second output circuits may further comprise first and second FETs, respectively. The means for outputting a first signal and the means for outputting a second signal may include means for ensuring that at least one of the first and second FETs is turned off.
As a further aspect of the invention, a code following apparatus for a pulsating rail current from a railway code transmitter comprises: a first terminal structured to input the pulsating rail current; a second terminal structured to output the pulsating rail current; first means for responding to the pulsating rail current flowing from the first terminal and for outputting a corresponding first signal, which turns on and off in response to the pulsating rail current; second means for responding to the pulsating rail current flowing from the first means and toward the second terminal and for outputting a corresponding second signal, which turns on and off in response to the pulsating rail current; means for determining that each of the first and second means is functional based upon the first and second signals and for outputting a third signal, which follows the pulsating rail current; and at least one output structured to follow the third signal.